For a project we hope to get, I have been researching extending WordPress. With WordPress 3 at Release Candidate 1 status, the new features included will be helpful… custom menus, custom post types, etc. So, I found this great tutorial on creating custom write panels over at wefunction.com. This way, WP could be extended to include metadata fields, right in the native interface. Sweet!
Also, there is a series of articles at Far In Space on metabox creation and display.